In an image forming apparatus employing a so-called “electrophotographic method” such as a digital copier and a laser printer, an image is formed by transferring a toner image onto a recording medium such as recording paper and by fixing the toner image onto the recording medium such as the recording paper by heating and pressing under predetermined conditions. In such an image forming apparatus, it is desired to determine desirable conditions of the heating and pressing when the toner image is fixed. Especially, to form a high-quality image, it may be desired to separately set the fixing conditions of the toner image in accordance with the type (kind) of the recording medium.
This is because the image quality to be recorded (formed) on the recording medium may be greatly influenced by, for example, the material, thickness, humidity, smoothness, coating condition and the like of the recording medium. For example, in terms of the smoothness, the convexo-concave degree of the recording medium may vary depending on the fixing conditions. As a result, a toner fixation rate may be decreased at a concave part of the recording medium, and accordingly, it may become difficult to acquire a high-quality image. Namely, if an image is formed without using an appropriate fixing condition which is to be determined based on the actual smoothness of the recording medium on which the image is to be formed, color irregularity may occur, and it may become difficult to acquire a high-quality image.
On the other hand, with a recent progress of an image forming apparatus and a diversification of the expressions, the number of the types of the recording sheets which become the recording media has been increased to more than several hundreds. Further, in each type of the recording sheets, there are so many brands in the recording sheets which differ from each other based on the basis of weight, thickness and the like. Due the differences, to form a high-quality image, it is desired to set fixing conditions in detail based on the type and brand of the recording medium such as the recording sheet.
Such recording media include plain paper, coated sheets such as a gloss coated sheet, a matt coated sheet, an art coated sheet, an OHP sheet, a special sheet having an embossed surface and the like. The number of the types and brands of the recording media is increasing. In the above examples, recording sheets are described as the examples of the recording media. However, it is noted that there are recording media which are other than the recording sheets.
On the other hand, even the latest image forming apparatus, the fixing condition of the image forming apparatus may be desired to be set by a user. Due to this, the user may have to have a knowledge of the various types of the recording media or the like. Further, the fixing condition may have to be set by the user, the user may feel uncomfortable because it is required to set the fixing condition by himself/herself. Further, if the fixing condition is not set correctly, a desired high-quality image may not be acquired.
To overcome the problem, research has been made to provide a sensor capable of identifying the type of a recording medium such as a recording sheet by automatically sensing the type of the recording medium such as the recording sheet and an image forming apparatus including such a sensor so as to automatically sense the type of the recording medium and is capable of forming an image.
For such a sensor for identifying (sensing) the type of a recording medium such as a recording sheet, there is a method, as described in Patent Document 1, in which a sensing probe is used to detect a surface friction resistance, and there is another method, as described in Patent Document 2, in which a pressure sensor or the like is used to detect the strength (stiffness) of the recording sheet. Further, as described in Patent Document 3, as a non-contact method of identifying the type of the recording medium, an imaging device such as an area sensor is used to capture an image of a surface of the recording medium to identify the type or the like of the recording medium based on the captured image.
Further, as a non-contact method of identifying the type or the like of the recording medium, there is a method using reflected light. In the method of using the reflected light, the light emitted from a light source such as a Light Emitting Diode (LED) is irradiated to the recording medium to be identified, and the type or the like of the recording medium is identified based on a reflected light amount from the recording medium. As the method of using the reflected light, there are three methods as described below.
In the first method, as described in Patent Document 4, the light amount of the reflected light is detected in the regular reflection direction of the light which is irradiated on the surface of the recording media to identify the brand or the like of the recording medium based on the detected light amount of the reflected light in the regular reflection direction. More specifically, in Patent Document 4, the brand of the recoding medium is identified by detecting the light amount in the regular reflection direction and the light amount of the light having passed through the recording sheet. Therefore, accurately speaking, the recording sheet is not identified based on the light amount in the regular reflection direction alone.
In the second method, as described in Patent Document 5, a plurality of light amount detecting units are used to detect not only the light amounts of the reflected light of the light irradiated on the surface of the recording medium in the regular reflection direction but also the light amounts of the scattered reflected light, so that the brand or the like of the recording medium is identified based on the detected light amount in the regular reflection direction and the light amount of the scattered reflected light.
In the third method, as described in Patent Document 6, the reflected light of the light irradiated on the surface of the recording medium in the regular reflection direction is divided by a polarization beam splitter to measure the light amount of the divided light, so that the brand or the like of the recording medium is identified based on the measured light amount.
Further, as a method of foreign matte inspection or the like, Patent Documents 7 and 8 disclose the inspection device and the inspection method.